This invention relates to the preparation of silane modified polysilacyclobutasilazanes from 1,1-dichloro-1-silacyclobutanes and certain difunctional nucleophiles. These materials are useful as intermediates to form crosslinkable preceramic polymers which, upon pyrolysis, yield ceramic materials.
What is disclosed herein is a novel process to obtain new and novel polymers which contain a strained ring silacycle in the polymer structure.
The process consists of forming silane modified polysilacyclobutasilazanes from polysilacyclobutasilazanes by reacting the polysilacyclobutasilazanes either with chlorosilanes, hereinafter defined, followed by treatment with ammonia or the simultaneous reaction of the ammonia and chlorosilanes with the polysilacyclobutasilazane.
Silazanes in general have been academic curiosities for many years and a variety of such silazanes, including monomers, oligomers, cyclics, low molecular weight and high molecular weight resins and linears have been prepared by a variety of methods.
For example, L. W. Breed, et al. in the Journal of Organic Chemistry, 27, 1114 (1962) report the formation of silazanes from the polymerization of sterically hindered silazane oligomers, while in the Journal of Polymer Science, A 2 45 (1964), cyclic trimer and tetramer silazanes are reported to be thermally cracked, using catalysts, to give linear polymers.
In contrast, fluids, rubbery polymers, and resins prepared from CH.sub.3 SiCl.sub.3, (CH.sub.3).sub.2 SiCl.sub.2, and excess ammonia have been reported by Kruger, et al. in the Journal of Polymer Science, A 2 3179 (1964).
The patent literature also contains disclosures of the preparation of silazanes. Cheronis in U.S. Pat. No. 2,564,674 discloses the preparation of low molecular weight linear silazane polymers by the reaction of halosilanes with excess ammonia in a solvent solution. Burkus, et al. in U.S. Pat. No. 3,892,713 discloses a similar reaction scheme with the added modification of removing the by-produced solid ammonium halide using ethylene diamine.
Verbeek, et al. in U.S. Pat. Nos. 3,853,567 and 3,892,583 disclose that mixtures of CH.sub.3 SiCl.sub.3 and (CH.sub.3).sub.2 SiCl.sub.2 can be treated with ammonia or organoamines to form materials that can be pyrolyzed to yield SiC/Si.sub.3 N.sub.4 ceramic materials. More recently, Gaul in U.S. Pat. No. 4,312,970, issued Jan. 26, 1982, disclosed the preparation of silazane polymers that were synthesized by reacting various alkyltrichlorosilanes with disilazanes such as {(CH.sub.3).sub.3 Si}.sub.2 NH. In his synthesis, (CH.sub.3).sub.3 SiCl was eliminated as a by-product. These materials can be pyrolyzed at high temperatures to form Si-C-N containing ceramics.
In addition, Gaul, in U.S. Pat. No. 4,404,153, issued July 20, 1982, disclosed preceramic polysilazanes which had been prepared by the reaction of chlorine-containing disilanes and disilazanes.
Cannady, in U.S. Pat. No. 4,543,344 discloses polymers prepared by reacting HSiCl.sub.3 and disilazanes and later, Cannady, in U.S. Pat. No. 4,540,803, issued Sept. 10, 1985, described a modification to Gaul's earlier process to include the preparation of a polyhydridomethylsilazane polymer from HSiCl.sub.3 and hexamethyldisilazane.
Polymers have been developed and disclosed by Gaul, in U.S. Pat. No. 4,395,460, issued July 26, 1983, and U.S. Pat. No. 4,404,153, issued Sept. 13, 1983; Haluska, in U.S. Pat. No. 4,482,689, issued Nov. 13, 1984; Seyferth, et al. in U.S. Pat. No. 4,397,828, issued Aug. 9, 1983, and U.S. Pat. No. 4,482,669, issued Nov. 13, 1984; Cannady, in U.S. Pat. No. 4,535,007, issued Aug. 13, 1985; Bujalski, in U.S. patent application Ser. No. 653,003 filed Sept. 21, 1984; Baney, et al. in U.S. patent application Ser. No. 652,938 filed Sept. 21, 1984 and U.S. patent application Ser. No. 653,939 filed Sept. 21, 1984; and Haluska, in U.S. patent application Ser. Nos. 926,145, filed Nov. 3, 1986, and 926,607, filed Nov. 4, 1986.
Further, in a copending application Ser. No. 059,718 filed on June 8, 1987 and entitled "Polysilacyclobutasilazanes," the inventor herein, Gary T. Burns, discloses the preparation of yet another new and novel class of silazane polymers: polysilacyclobutasilazanes prepared from 1,1-dichlorosilacyclobutanes and certain nitrogen containing difunctional nucleophiles.
In spite of an intensive search, however, the inventor herein was not able to find any suggestion or teaching in the art regarding the formation of silane-modified polysilacyclobutasilazanes. This invention is based on the utilization of such polysilacyclobutasilazanes as a precursor to still another type of new and novel silazane polymer.